The present invention relates to meltblown superabsorbent, thermoplastic polymeric compositions. More particularly, the present invention relates to nonwoven webs prepared by meltblowing superabsorbent, thermoplastic polymeric compositions.
Meltblowing techniques for forming nonwoven webs or materials from the random deposition of relatively small diameter fibers from thermoplastic resins is well known in the art. For example, the production of fibers by meltblowing is described in an article by Van A. Wente, entitled, "Superfine Thermoplastic Fibers," which appeared in Industrial and Engineering Chemistry, Vol. 48, No. 8, pp. 1342-1346 (1956). The article was based on work done at the Naval Research Laboratories in Washington, D.C. See also Naval Research Laboratory Report 111437, dated Apr. 15, 1954. A more recent article of a general nature is Robert R. Butin and Dwight T. Lohkamp, "Melt Blowing--A One-Step Web Process for New Nonwoven Products", Journal of the Technical Association of the Pulp and Paper Industry, Vol. 56, No. 4, pp. 74-77 (1973).
In general, meltblowing techniques include heating a thermoplastic, fiber-forming resin to a molten state and extruding the molten resin as threads from a die having a plurality of linearly arranged small diameter capillaries. The molten threads or filaments exit the die into a high velocity stream of a heated gas which usually is air. The heated gas serves to attenuate, or draw, the threads of molten resin to form fibers having diameters which are less than the diameter of the capillaries of the die. The fbbers thus obtained usually are deposited in a random fashion on a moving porous collecting device, such as a screen or wire, thereby resulting in the formation of a nonwoven web. By way of illustration only, some specific examples of meltblowing techniques are described in U.S. Pat. Nos. 3,016,599, 3,755,527, 3,704,198, 3,849,241 and 4,100,324.
Meltblown webs are particularly useful in the manufacture of disposable absorbent products such as diapers, sanitary napkins, tampons, incontinence products, and the like. Such products typically are comprised of a batt or absorbent portion which is wrapped with a liner. The batt typically is comprised primarily of cellulose fibers and the liner usually is a nonwoven web of a polyolefin such as polyethylene or polypropylene.
In the past, significant efforts have been made to find ways to make such disposable absorbent products more efficient or more appealing to the consumer. Much of such efforts have focused on increasing the absorbent capacity of the product on a unit mass basis while at the same time increasing the ability of the product to retain absorbed fluid. The ability of a product to remove and keep body fluids from the skin is perceived as a desirable attribute and is believed to be a factor in the reduction of such skin problems as diaper rash.
Such increased absorbent capacity and fluid retention typically have been accomplished by incorporating a superabsorbent material into the absorbent batt. The superabsorbent material usually is in particulate form. Unfortunately, particulate superabsorbents often migrate in or fall out of the absorbent product and/or exhibit gel-blocking, a phenomenon which prevents the migration of fluid into the central portion of the superabsorbent particle. Furthermore, the use of the particulate superabsorbent introduces unique problems into the manufacturing process. Finally, rather high levels of superabsorbent in the absorbent batt often are necessary in order to result in significant improvements in wicking rates and retention capacities, and the superabsorbent particles often migrate out of the absorbent batt.
It is expected that all of the foregoing difficulties encountered through the use of particulate superabsorbents in disposable absorbent products can be minimized or even eliminated if the superabsorbent were in the form of a nonwoven web. However, superabsorbent nonwoven webs are believed to be unknown prior to the present invention, even though there is a large body of literature relating to superabsorbents and to products into which superabsorbents have been incorporated.
Superabsorbent materials, also referred to as hydrogels, frequently are based on acrylate and methacrylate polymers and copolymers. Other hydrogels are based on starch or a modified starch. Hydrogels prepared from hydrolyzed crosslinked polyacrylamides and crosslinked sulfonated polystyrenes or based on maleic anhydride (or similar compounds) have been described. Finally, still other hydrogels are based on polyoxyalkylene glycols and include polyurethane hydrogels.
The known polyoxyalkylene glycol-based superabsorbents generally tend to come within one of the following classes, at least in so far as they are reasonably related to the present invention:
(1) crosslinked poly(oxyalkylene) glycols; PA0 (2) crosslinked isocyanate-capped poly(oxyalkylene) glycols, i.e., polyurethanes or polyureas; PA0 (3) polyurethanes prepared from polyfunctional prepolymers or resins and diisocyanates; PA0 (4) polyurethanes prepared from isocyanate-capped polyesters or poly(oxyalkylene) glycols and difunctional extenders; PA0 (5) polyurethanes prepared from poly(oxyalkylene) glycols, isocyanate-capped low molecular weight prepolymers, and polyfunctional low molecular weight components.